How Can I Efficiently Extend a JavaScript Array In-Place?

Extending JavaScript Arrays: An In-Place Solution

Extending an existing JavaScript array with another array without creating a new one is not a straightforward operation. Unlike Python's extend method, JavaScript does not provide a built-in solution.

Fortunately, we can achieve this behavior efficiently using the .push() method in conjunction with the spread operator(...).

const a = [1, 2];
const b = [3, 4, 5];

a.push(...b);

The spread operator expands the elements of b into individual arguments, passing them to a.push(). This effectively adds the entire contents of b to a.

Alternatively, in older browsers that do not support ECMAScript 6, you can use the .apply() method:

a.push.apply(a, b);

However, this approach may fail due to stack overflow errors when the number of elements in b is excessive. In such cases, a traditional loop-based technique is recommended:

for (const element of b) {
  a.push(element);
}

This ensures that the elements are appended to a one by one, avoiding the stack overflow issue.

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